1. Field of the Invention
The present invention relates to a three-phase alternating current motor, and more specifically relates to, in fractional-slot motors having complicated winding arrangements, a three-phase alternating current motor having a wave winding configuration.
2. Description of Related Art
Conventionally, there are known fractional-slot motors in which the division of a slot number by a pole number is a fraction in lowest terms, as a combination of the pole number and the slot number that allows a reduction in torque ripple of the motor.
In the fractional-slot motors, the pole number and the slot number can be determined such that the pole number and the slot number have a high least common multiple and a high-order distributed winding factor is lowered. Therefore, the torque ripple can be reduced.
Also, in the fractional-slot motors having a slot number, i.e., three or more times higher than the number of pole pairs, although the torque ripple tends to decrease, a coil pitch of windings to be inserted into slots is larger than one slot (the distance between the adjoining slots) and hence only distributed winding is available. Especially, motors in which the division of a slot number by the number of pole pairs is a fraction in lowest terms each have a complicated winding configuration and an increased number of coils of windings to be inserted into slots, thus being unsuitable for automation of a winding step in manufacture.
The increased number of coils requires long coil ends, in order to avoid interference among the coils or interpose interphase insulating sheets each between the coils. The long coil ends cause an increase in the dimensions of a motor body. Also, the long coil ends increase the windings in length, thus causing an increase in a winding resistance of each phase.
Furthermore, the increased number of coils increases the number of connecting wires between the coils, thus causing complicated intertwinement of the windings with each other.
As an example of methods for manufacturing stators of motors, there is known a manufacturing method using an automatic winding machine having an inserter (For example, Japanese Unexamined Patent Publication (Kokai) Nos. 2013-183492, 2002-165396, and 2001-238414). In this method, a plurality of coils is manufactured by turning nozzles or fliers of the winding machine about spools. The manufactured coils are inserted into the inserter, and the inserter is gradually inserted into a stator so that the coils are wound in the stator. In this process, an increase in the number of coils to be manufactured increases the number of insertions into the inserter, and thus significantly increases the number of manufacturing steps. Also, since a lot of coils are inserted into the inserter, when there are a number of connecting wires between the coils, windings may be complicatedly intertwined and cause a manufacturing failure.
The manufacturing method using the inserter has the following problems.
Fractional-slot winding motors having complicated winding configurations are difficult to be manufactured by automatic winding and require a number of manufacturing steps.
An increase in the number of coils increases overlaps of the coils and increases the length of coil ends.
An increase in the number of coils increases the number of connecting wires between the coils and causes complication.